The operation couldn't be performed because object couldn't be found on 'xxx.prod.outlook.com'

The object has not been replicated to Office 365, check Dirsync error logs, dirsync email errors. Ensure these errors have all been resolved before the users are added to migration list and ensure the object has been sync’d to O365

To be able to use the -DeleteContent Parameter you need to have "Mailbox Import Export" permissions. Without these permissions, the parameter -DeleteContent is not available for the Search-Mailbox Command.

Instructions:

1. Create a new Security Group

2. Enter the following command in Exchange Management Shell (replace the Security Group name accordingly):

The issue occurs when migrated accounts cannot clear homemdb, homemta, msexchhomeservername and msexchguid attributes from the source server and set the TargetAddress on the source side which it is supposed to do after mailbox move completes (flipping of the attributes starts after 95% completion of the move). A script can be created or apply this hotfix - http://support.microsoft.com/kb/940012

Error: This mailbox exceeded the maximum number of large items that were specified for this request. --> MapiExceptionMaxSubmissionExceeded: IExchangeFastTransferEx.TransferBuffer failed (hr=0x80004005, ec=1242)

If you receive the following error when trying to migrate to O365, the you will need to check that your EWS endpoints are published correctly.

The call to 'https://mail.company.com/EWS/mrsproxy.svc' timed out. Error details: The request channel timed out while waiting for a reply after 00:00:00.Increase the timeout value passed to the call to Request or increase the SendTimeout value on the Binding. The time allotted to this operation may have been aportion of a longer timeout. --> The HTTP request to https://mail.company.com/EWS/mrsproxy.svc' has exceeded the allotted timeoutof 00:00:00.0010000. The time allotted to this operation may have been a portion of a longer timeout.--> The operation has timed out

Without stating the obvious, there is a timeout issue! I have seen before if you haven’t published EWS correctly to the internet. Ensure when you connect to https://mail.company.com/EWS/mrsproxy.svc that you get prompted for authentication from the exchange server and there is no pre-authentication at TMG/UAG for example. Once EWS is published to the internet correctly you should be able to start migrations to O365!